Electrical gaseous discharge device



July 26, 1938. P. L. SPENCER 2,124,632

ELECTRICAL GASEOUS DISCHARGE DEVICE Filed May 19, 1952 2 Sheets-Sheet 1uuuuunn E621.

mom/Er Patented July 26, I938 UNITED STATES PATENT OFFICE ELECTRICALGASEOUS DISCHARGE DEVIC of Delaware Application May 19, 1932, Serial No.612,235

28 Claims.

This invention relates to gaseous discharge devention will be bestunderstood from the following description of exemplifications thereof,reference being had to the accompanying drawings, wherein:

Fig. 1 is a cross-sectional view of one embodiment of my inventionshowing a discharge device with one cathode and one anode, together witha diagrammatic representation of a circuit which may be used therewith;

Fig. 2 is a view similar to that of Fig. 1, showing a different form ofdischarge device having one cathode and two anodes;

Fig. 3 is a similar view showing a discharge device having two cathodesand one anode; and

Figs. 4, 5 and 6 are curves for analyzing the relationships between thecurrent, voltage and magnetic variations.

In Fig. 1, i represents a hermetically-sealed glass envelope having anenlarged chamber 2 at one end thereof within which is supported athermionic cathode 3 at the inner end of a reentrant stem 4. The cathode3 is supported by two lead-in wires 5 and 6 which pass through and aresealed in the inner end of the reentrant stem 4. The cathode preferablycomprises a metallic filament, such as, for example, nickel coated withsome material to increase the electron emissivity of said filament. Sucha coating may consist, J for example, of barium or strotium oxide. Atthe opposite side of the chamber 2 from the stem 4, the envelope I isformed to provide an elongated tubular section I. At the opposite end ofthis tubular section from the cathode 3, is provided a cooperating anode8 supported at the inner end of a reentrant stem 9. The anode 8 ispreferably supported by an anode lead I passing through and being sealedin the end of said stem 9. The "anode 8 is formed of some suitablerefractory conducting material, such as, for example, graphite, carbon,tantalum, or carbonized nickel. Interposed between the cathode 3 and theanode 8 and surrounding the discharge path between them is provided aconductive tubular member Ii. The tubular member II is made ofnon-magnetic material, and preferably comprises a cylinder of thin sheetmetal, such as, for example, tantalum. Member ll may be of any othersuitable form, such as, for example, a wire mesh or a metallic depositon the walls of the tubular section 1. Also it is possible to make it sothat it does not completely surround the discharge path within it. Thetubular member ll preferably fits snugly within the glass tubularsection 1, whereby said tubular member II is supported by the walls ofsaid tubular section I. A lead-in wire l2 also sealed through the end ofthe reentrant stem 9 and electrically connected to the tubular member llaflords an external electrical connection to said member. In order toprotect the inner end of the reentrant stem 4 against the energygenerated by the discharge between the cathode and anode, there isprovided a shield I3 supported by one of the cathode leads, such as, forexample, 5. The other cathode lead 6 passes through an opening I4 insaid shield. The envelope I after being thoroughly evacuated inaccordance with the usual practice is provided with some suitablegaseous filling which may be, for example, a metallic vapor, such asmercury vapor. In order to supply this vapor, a small quantity ofmercury 15 is introduced into the tube. Of course it is to be understoodthat any ionizable gas, such as, for example, one of the noble gases,may be used as the filling within the envelope I. Furthermore, anysuitable mixture of gases and vapors may be utilized in the device. Inorder to supply power to the device, there may be provided a supplytransformer l6 having a primary l1 and a secondary I 8. The filament 3may be provided with heating current by a section I9 at one end of thesecondary l8. The opposite end of the secondary 18 may be connected bymeans of a conductor 28 through any desired load device 2| to the anodelead Ill. The lead-in wire I2 for the tubular member II is connectedthrough a resistance 22 to the anode lead-in l0. Resistance 22 is ofcomparatively .high value, for example, of the order of about one-half amegohm in order to limit the current to the member II to a negligiblevalue. It will be seen that upon energization of the transformer IS, thefilament 3 will be supplied with heating current, whereby it will beraised to a temperature at which it emits a copious supply of electrons.When the anode 8 becomes positive, these electrons will travel towardsaid anode, producing an intense ionization of the gas within theenvelope, whereupon a current of large value will flow between the anode8 and the cathode 3. I have discovered in such a device that if amagnetic field is applied transversely to the discharge path between theanode 8 and the cathode 3, no current will pass between these electrodeswhen the magnetic field atta'ms a comparatively low value Thistransverse magnetic field may be applied in any suitable manner. Forexample, in Fig. l, I have shown a magnet 23 external to the tube.adjacent the tubular member Ii, suitably positioned so that its fieldpasses into the discharge space between the'cathode 3 and anode 8transversely thereto. Since the value of the magnetic field at which thetube will not conduct is fairly critical, I prefer that the magnet 23 bebiased, as, for example, by having it in the form of a permanent magnet,so that its normal field is slightly below the critical value at whichthe tube ceases to conduct. The magnet 23 could, of course, have anauxiliary winding (not shown) to bias it to the proper value ofmagnetization. In order to provide means for controlling the magnitudeof the magnetic field, I provide a coil 24 wound around the magnet 23and energized from some suitable source of current, such as, forexample, a battery 25. The magnitude of the current through the coil 24and consequently the magnetic field may be controlled by some suitablemeans, such as an adjustable resistance 28.

In the device as described above, I have found that when the magneticfield is below a certain minimum, current will fiow between the anode 8and the cathode 3, whenever the anode 8 is positive, and therefore arectified current will fiow through the load device 2|. As the magnitudeof the field is increased by means of regulating the adjustableresistance 28, the amount of current flowing through the load device 2igradually decreases in value until when a certain maximum field isreached the tube is entirely non-conducting and substantially noresultant current flows through said load device.

According to my present understanding of the theory of operation of thedevice, it operates as follows. When the anode 8 and tubular member Hbecome positive, a small space current fiows between the cathode 3 andthe end of the tubular member ll adjacent said cathode. This current mayordinarily be of the order of about one-tenth of a milliampere. Inasmuchas these tubes are designed to handle currents of the order of amperes,this space current is so small as to be practically negligible insofaras the load device is concerned. However, this small amount of currentmakes a comparatively large number of ions in the region between thecathode 3 and the end of the tubular member H.- The member ll being ofconductive material forms an electrostatic shield around the spacewithin it. Thus the intensity of the electrostatic field, due to the-negative charge on the cathode, decreases very rapidly as we go downthe tubular member l| toward the anode. Likewise the electrostaticfield, due to the positive charge on the anode, decreases very rapidlyas we go up the tubular member i I toward the cathode. With ordinaryvalues of voltage, a portion within the tubular member intermediate theanode and cathode can be said to be substantially electrostaticallyfield free. Under these conditions the intensity oi ionization decreasesvery rapidly as we go down the tubular member from the cathode towardthe anode 8. There are a very few of the electrons existing within thetubular member ll, however, which come under the influence of thepositive charge on the anode 8. As the voltage on the anode becomesgreater, its positive charge increases. As the positive charge on theanode increases, its electrostatic field will increase in intensityinside of the tubular member H, and a larger number of electrons willcome under its influence. If enough of these electrons come under theinfluence of this charge, cumulative ionization results and the fullcurrent flows. Cumulative ionization may be explained as follows. Anelectron coming under the influence of the charge or field of the anode8 is accelerated toward the anode, and may acquire. sufilcient energy toionize an atom of gas upon collision therewith, whereupon it is againaccelerated to ward the anode. There is, however, some difiusion to thewalls of the tubular member ll of electrons, whether coming from thecathode 3 or being liberated as the result of the ionization of gasatoms. The electrons reaching the walls of. member ll fiow out of thetube through the lead wire i2, and are thus removed or lost from thedischarge path between the cathode and the anode. If the rate at whichelectrons are lost to the member II is greater than the rate at whichelectrons are liberated as a result of the ionization of gas atoms,cumulative ionization cannot occur and the discharge does not start. If,however, the rate at which electrons are so lost is less than the rateat which electrons are liberated, cumulative ionization does occur andthe discharge starts. Upon the starting of a discharge the intensity ofionization along the entire discharge path increases enormously, and alarge current flows between the cathode and anode. In absence of atransverse magnetic field, the rate of loss of electrons in the deviceas shown is ordinarily less than that which will prevent cumulativeionization, and the discharge will start very soon after the beginningof each half of the alternating current cycle when anode 8 becomespositive. When the transverse magnetic field, due to the magnet 23, isimpressed on the device, this field acts upon electrons which comewithin the tubular member and which otherwise might proceed toward theanode 8 to push them over against the walls of the tubular member II,and thus increases the rate at which the loss of these electrons to themember ll occurs. It will be seen that the ease with which the electronsare controlled by the magnetic field is particularly great in theelectrostatically field-free space referred to above. The pushing of theelectrons overagainst the walls of the tubular member ll moves theentire region of more intense ionization over against these walls, andthus an electron cannot undergo many ionizing collisions before it iscaptured by the wall of member ll. Also the electrons liberated as aresult of. such ionizing collisions are liberated close to the walls ofmember II, and are also soon captured by it, all of which greatlyincreases the rate of the loss of electrons to the member I I. This rateof loss increases with the magnitude of the magnetic field. Thus witheach definite value of voltage, when the field becomes strong enough,the rate of loss of electrons becomes so great that cumulativeionization is impossible, and therefore the discharge will not start.However, any lesser value of field does not produce a sufiicient loss ofelectrons to prevent cumulative ionization, and consequentiy thedischarge starts between cathode 3 and anode 8. The control of.ionization'which is aiforded by such a magnetic field may be termed acontrol of the propagation of ionization along the discharge pathbetween the cathode and anode. As soon as the discharge begins, theenormous increase in ionization referred to above occurs and a largecurrent flows between the cathode and anode. Since the intensity ofionization and consequently the rate at which electrons are liberatedincreases so enormously, a magnetic field which may be sufficientlylarge to prevent the start of a discharge will ordinarily be unable toincrease the rate of electron loss to a sufllcient degree to stop thedischarge after it has once started.

It should be noted that although the above analysis refers to the losselectrons to the walls of member H, the same eflect exists al- ,thoughto a lesser degree with respect to positive ions within the spacesurrounded by the tubular member. These ions are not only captured bythe walls of member II by diflusion thereto, but are also acted upon bythe magnetic field to tend to push them over against the walls .ofmember II. The removal of positive ions from the discharge path removesadditional current carriers, and therefore decreases the tendency of adischarge to start. Therefore, it is to be understood that whenever Irefer to the loss of electrons to the walls oi member II, I also meanthat the same thing to a lesser degree is occurring to positive ions.The manner in which the magnetic field controls the magnitude of thecurrent fiowing through the load device 2| may be seen more clearly byreferring to Fig. 4. In this figure, curve a represents the variation ofvoltage applied between the cathode 3 and the anode 8 with respect totime. Since we can assume. for the purposes of analysis that the load Itis a resistance load, each point on this curve can represent the amountof current which would 5 flow through the circuit if the device wereconducting at that point. When the field, due to the magnet 23 and theelectromagnetic coil 24, is below a certain minimum, the device asstated above becomes conducting whenever the anode 8 is positive. Thus,the device is conductive between the points I; and c of a single voltageand current cycle during which time the anode 8 is positive, and isnon-conductive between points 0 and (1 during which the anode 8 isnegative. Although in each of my curves I have shown the dischargestarting at zero voltage and stopping at zero voltage, actually thevoltage must rise to a small starting value before the discharge willstart, and will fall to a value just below the tube drop voltage whenthe discharge will stop. Since in comparison with the operatingvoltages, these values are quite small, they may be considered as zeroat least for purposes of illustration. As the value of the magneticfield is increased by a certain amount, the rate of loss of electronsbecomes so great that suflicient electrons to produce cumulativeionization do not come under the influence of the field on anode 8 untilthe voltage on the anode reaches the point e on curve a, and thus thetube will not "become conductive until the voltage between the Y anodeand cathode reaches this point. Under these conditions, the tube willonly conduct between the point 1, at which the voltage reaches 65 thevalue e, and the point e at the end of that half of the voltage cycle.As the magnetic field is further increased by a certain amount, the rateof loss of electrons becomes still greater so that the tube does notstart to become conductive until the voltage between the anode and thecatl'rode reaches a value of g on the voltage curve n. Thus the tubeonly conducts from the point h, at which the voltage attains the valueg, and the point e at the end of that half of the voltage cycle. Thefield may be further increased until finally the tube does not becomeconductive until the voltage between the anode' and the cathode reachesits maximum value i. Thusthe tube only is conductive through a quarterof a complete voltage cycle, namely, from the point i at which thevoltage reaches its maximum value and -the point e at the end of saidhalf of the voltage cycle. If the magnetic field is increased beyondthis point, the tube can never become conductive inasmuch as it wouldrequire a voltage greater than the peak value of the voltage between theanode and cathode to start the discharge. It can be seen that when thetube is conductive only during a portion of the positive half of thevoltage cycle, the

resultant value of current flowing through the load device becomes lessas the portion 01' said positive half of the voltage cycle during whichthe current fiows becomes less. Since, as shown above, the magnitude ofthe magnetic field determines the portion of the voltage cycle duringwhich the tube is conductive, by controlling the magnitude of themagnetic field we can con- :Iige the amount of current flowing throughthe The provision of the tubular member ll between the cathode and anodeperforms various important functions. If we were to attempt to controlthe current between the cathode and anode by a transverse magnetic fieldwithout the provision of such an element as the tubular member II, wecould obtain some increase in the loss of ions created in the spacebetween the cathode and anode by forcing electrons over against theglass walls of the tube by means of said transverse magnetic field.These electrons upon reaching the walls of the tube would charge itnegatively. This charge, however, can only be removed by theneutralization thereof by positive ions created within the dischargespace. Since these positive ions are relatively heavy and. diffusesomewhat slowly, the negative charge upon the walls of the tube becomesfairly large and repels any additional electrons which may be forcedover against the walls of the tube by the magnetic field. Thus the rateat which electrons can be withdrawn from the discharge path is much lessin such a device than with the provision of a conductive tubular membersurrounding the discharge space. ber H is conductive and is connected tolead the electrons and positive ions which it captures out of the tube,the rate at which these current carriers can be removed from the path ofthe discharge is greatly increased. This efiect can be obtained to somedegree even if ,the member.

ll does not completely surround the discharge path, as shown, andconsists merely of a conductive member of extended area placed adjacentthe discharge path. Further, in the absence of such a conductive tubularmember, as H, the electrostatic field from the anode 8 can act freelyacross the whole space, and thus exert a very strong influence upon theelectrons throughout this entire space. However, the tubular member llacts as an electrostatic shield so that the field of the anode 8 canextend effectively only a short distance within said tubular member I l.Therefore, the loss of electrons by being forced over against the wallsof the tubular member may be small enough so that there is aconsiderable number of free electrons left within the tubular member ll,yet due to the electrostatic shielding of this member, the field of theanode 8 is not strong enough to influence these Since the memof two andone-half inches.

electrons to any considerable desree. Under these conditions, theseconsiderable number of electrons may exist within the tubular member ii,and yet cumulative ionization will not occur. This effect likewiseexists even though the member Ii does not completely surround thevdischarge space. As long as the member Ii accomplishes someelectrostatic shielding of the discharge path, the above advantageexists in some degree. Thus the control of the discharge by a transversemagnetic field becomes a comparatively simple matter by the provision ofthe conductive tubular member H while it is a matter of considerabledifficulty without such a member. In one of the tubes which I haveconstructed in accordance with the above disclosure,

I used a tubular member ii having a diameter of one and one-quarterinches and a length In this tube, when 110 volts of alternating currentare applied between the cathode 3 and anode 8, current flowed freely.However, when a transverse magnetic field of about thirty gauss wasapplied, the current ceased. Merely a change in this transverse magneticfield of about three gauss was sufllcient to change the tube from aconducting to a nonconducting state. This tube operated satisfactorilywith a filling of mercury vapor at pressure broadly between .001 mm. and.01 mm. of mercury. If it is desired to use higher pressure within thetube, the tubular member II should be made longer or of smaller diameteror both. The pressure in the tube can be controlled by properlyproportioning the external area of the glass envelope or by providingadditional condensing chambers removed from the path of the discharge.Tubes have been constructed in which variations of about one-quarter ofa watt have been sufllcient to control two kilowatts of power directly.

Instead of having a tube with but a single cathode and a single anode,it is often desirable to construct such a device having two anodescooperating with the cathode. Such an arrangement is shown in Fig. 2. Inthis figure a hermetically sealed envelope 21 encloses a thermioniccathode 28 similar to the cathode 3 in Fig. 1 and similarly supportedwithin an enlarged chamber 29. -The envelope 2'! is provided with twoelongated tubular sections 30 extending from opposite sides of thechamber 29. At the oppos te end of each of these tubular sections is ananode 3i cooperating with the cathode 28. Each of these anodes issimilar to the anode 8 in Fig. 1, and is similarly supported. Interposedbetween each of the anodes 3i and the cathode 28 within each of thetubular sections III is a tubular member 82 similar to the tubularmember ii, as shown in Fig. 1, and likewise similarly supported. Thetubular members may extend up around the anodes 3i if it is desired toshield the discharge paths adjacent the anodes from charges on the glasswalls of the tube. Such an arrangement, however, is not necessary, thearrangement in Fig. 1 being equally as satisfactory. The interior of theenvelope 2'! is provided with a, suitable gas filling, as set forth forFig. 1, which filling may be a vapor supplied, for example, from aquantity of mercury 33 within the envelope 21. are connected to itscorresponding anode 3i through resistance 34 corresponding to theresistance 22 in Fig. 1.

The device in Fig. 21s supplied with a power from a supply transformer35 having a primary Each of the tubular members 32 3| and a secondary31, the opposite ends of which are connected to the anode leads 88, eachconnected to its respective anode 8|, The cathode 28 is supplied withheating current from a heating transformer 88 having a primary 48 and asecondary 4i, which secondary is connected at opposite ends to the twocathode leads 42 and 43. A point intermediate the ends of the secondary31, which is preferably the mid-point thereof, is connected through somesuitable load device 44 to the cathode 28. This connection may becompleted, for example, by a connector leading to a point intermediatethe ends of the secondary 4i, which point is preferably at the center ofsaid secondary. It will be seen that upon energization of thetransformers 35 and 38, current will flow during alternate half cyclesbetween the cathode 28 and one and the other of the two anodes 8i. As aresult, a rectified current will fiow through the load device 44.Instead of but a half cycle of the alternating voltage wave beingutilized, as is the case in Fig. 1, both halves of the alternatingvoltage cycle are rectified, producing a more uniform fiow of currentthrough the load device. In order to control the fiow of current betweeneach of the anodes 3i and the cathode 28, I have provided two magnets 45each similar to the magnet 28 in Fig. 1, and each also provided with acontrol coil 46 similar to the control coil 24 in Fig. 1. Each of thecontrol coils 46 may be energized by a controlled direct current, as isthe case in Fig. 1, whereupon the current between each of the anodes 2iand the cathode 28 is controlled as explained for Fig. 1. If, however isis desired to utilize alternating current for the energization of eachof the coils 46, this may be accomplished, for example, by means of sucha circuit as is shown in Fig. 2. In this arrangement, the two coils 46are connected in series across the two terminals of the secondary 31. Inthis series connection are placed one or more condensers 41 of a valueto make this series circuit substantially resonant to the frequency ofthe applied voltage. Thus the current flowing through the coils 46 andconsequently the variation in the magnetic field will be substantiallyin phase with the voltage applied between each of the anodes 3i and thecathode 28. However, I wind my coils 46 in such a direction that thevariation in magnetic field takes place in the opposite direction to thevariation in voltage between the corresponding anode and the cathode. Ialso bias the initial and average magnetization of each of the magnets45 to a certain definite value, either by providing auxiliary permanentmagnets (not shown) or additional energizing coils 48 fed by directcurrent from a battery 49, and cooperating with each of the magnets 45.To prevent the oils 46 from inducing excessive currents in coils 48, Iprovide a choke 48' in series with the coils 48. In order to control themagnitude of the current through each of the coils 46 and the consequentmagnitude of magnetic variation, I provide an adjustable resistance 58in the above-mentioned series circuit. The manner in which the resultantvariation in the magnetic fields of each of the magnets controls themagnitude of the discharge in the tube, can be best understood byreferring to Fig. 5. In Fig. 5 curve It represents the variation involtage applied between one of the anodes 3i and the cathode 28, and aswith Fig. 1, assuming that the load 44 is a resistanceload for thepurpose of analysis, each point on this curve can represent the amountof current which would fiow from the load if thedevice were conductingat that point. The voltage between the other anode and the cathode is,of course, out of phase with the voltages represented by curve It. Atsome value of magnetic field, which may be represented by the line I,the loss of electrons to the corresponding tubular member 32 decreasesto such a point that the discharge is able to start. Under suchconditions, each of the magnets 45 is biased so that its initial andaverage value of magnetization, which may be represented by the line111., is greater than the value represented by I. At some setting of theadjustable resistance 5|), the variation in magnetic field due to thevariation in the coil 46 follows the curve 11. It will be seen that withthis variation of the magnetic field, the value 1 is reached when thevoltage curve 76 has progressed through a quarter of its entire cycle.The discharge path between the corresponding anode 3| and the cathodethus becomes conducting at this point, which may be represented at o,and the discharge continues to the point p at the endof that half of thevoltage cycle. If the resistance 50 is adjusted so as to decrease thecurrent through the coil 46 and the consequent decrease in the magnitudeof the variation of the magnetic field, it will be seen that themagnetic field never decreases to the value I, and therefore thedischarge will not start between the corresponding cathode and anode.If, however, the resistance 50 is adjusted so as to increase the currentthrough the coil 46, and consequently the magnitude of the magneticvariation, the field of the magnet 45 will follow some such curve as maybe represented by q. Under these conditions the magnetic field willreach the value I sooner in the voltage cycle 16 than before. Thus thedischarge path between the corresponding anode and cathode will becomeconductive at the point r at which the magnetic variation q reaches thevalue I, and this discharge path will continue to be conductive fromsaid point r to the point p at the end of that half of the voltagecycle. As the value of the current through 46 increases as a result ofthe adjustment of the resistance 50, the corresponding discharge pathwill become conductive sooner during the voltage cycle. Thus, asexplained for Fig. 4, the resultant value of current through therespective discharge path can be controlled by controlling theadjustable re sistance 50. The analysis applies with equal force to thedischarge path between theopposite anode and the cathode, except thateach of the variations is displaced exactly 180 from that as shown inFig. 5. Thus each half of the voltage cycle is directed through the loaddevice 44 in the same direction, and is controlled as explained above.

Instead of utilizing two anodes with a single cathode, it may bedesirable to utilize a tube having two cathodes cooperating with asingle anode. 3. In this figure a hermetically sealed envelope 5|encloses two thermionic cathodes 52 at each end thereof. Each of thesecathodes is contained within an enlarged chamber 53, and is supported atthe inner end of a reentrant stem 54. Although these cathodes. may be ofthe filamentary type, as disclosed in Figs. 1 and 2, yet in someinstances I prefer to use an indirectly heated type of cathode inasmuchas such acathode can be operated more efficiently and with Such anarrangement is shown in Fig.

a greater electron emission. Each of the oathodes 52 consists of ahollow member 53' closed at one end and carrying a series of radial fins54' on the outside. thereof. Both the fins and the external surface ofthe member 53 are preferably covered with a material to increase'theirelectron emissivity, which material may be, for

example, the oxides of alkali earth metals. In order to heat theelectron emitting surfaces to their emitting temperature, a heatingfilament 55 is provided within the hollow member 53'. This heatingfilament is supported within said hollow member by means of filamentleads 56 and 51 sealted through the end of the reentrant stem 54. Inorder to prevent undue radiation of heat from the electron-emittingsurfaces and. thus maintain them more efliciently at their emittingtemperature, a metallic heat shield 58 is provided which surroundshollow member 53' and its fins 54', and is mechanically connected tosaid hollow member at one end thereof. The entire cathode structure maybe supported by two wires 59 and 60 also sealed in the end of thereentrant stem 54, one of which wires, for example so, may extendthrough the end of said reentrant stem and form an external electricalconnection .for the cathode. Intermediate the ends of the envelope 5| atsubstantially the center point of a tubular section 6| thereof, Iprovide a single anode 62. This anode is made of some suitablerefractory conducting material, such, for example, as specified for theanodes in Figs. 1 and 2. The anode 62 is supported at the inner end of areentrant stem 63 by means of an anode lead 64 sealed in the end ofsaid...

stem. Interposed between each of the cathodes and the opposite faces ofthe anode 62 are tubular members 65 similar to the tubular members IIand 32 in Figs. 1 and 2.- These tubular members 65 are supported withinthe tubular section 6| substantially as are the tubular members referredto in Figs. 1 and 2. Each of the tubular members 65 is provided with alead 66 sealed in the end of the reentrant stem 63, and affording anexternal electrical connection for each of said tubular members. It isdesirable to prevent electrons and positive ions from passing from thedischarge space on one side of the anode to the discharge space on theopposite side thereof. If this is not done, ions created in onedischarge path pass into the other discharge path, and a considerablenumber of ions exist near the anode at the start of the active cycle insaid other discharge path. The presence of these ions increases thetendency of the discharge to start, and renders the control by themagnetic field more difficult. In order to prevent this drawback, theends of the tubular members 65 adjacent the anode 62 are brought fairlyclose to the surface thereof at a distance so that passage of electronsor positive ions from one side of the anode to the other issubstantially prevented. In order that this passage of electrons andpositive ions be more completely prevented, the anode 82 is preferablymade somewhat larger than the inner diameter of each of the tubularmembers 65 so as to effectively shield the discharge path on one side ofsaid anode to the discharge path on the opposite side thereof. Theinterior of the envelope 5| is provided with suitable gas filling, suchas set forth for Figs. 1 and 2. Each of the tubular members 65 isconnected to the anode through a resistance 12 corresponding to theresistances 22 and 34 in Figs. 1 and 2.

' the secondary 63.

In order to supply the device in Fig. 3 with power, I have provided apower transformer 'I having a primary 68 and a secondary it. .Each ofthe heating filaments BI is supplied with heating current from sections10 at opposite ends of The cathode-emitting surfaces may be connected toopposite ends of the secondary 68, for example, by having the oathodelead 60 electrically connected to one 01 the heating filament leads 51.A point intermediate the ends of the secondary 88, which is preferablythe mid-point thereof, is connected through some suitable load device Hto the anode lead 64. It will be seen that upon energization of thetransformer 61, current will flow during alternate half cycles betweenthe anode 62 and \one or the other of the cathodes 52, whereuponarectified current will flow through the load device H. In order tocontrol the flow of current between each of the cathodes 52 and theanode 62, I have provided two magnets 13 similar to the magnets 45 inFig. 2. Each of these magnets is provided with a control coil Hi similarto the coils in Fig. 2. The magnetization of each of the magnets may becontrolled in any desired manner, for example, either' by such anarrangement as shown in Fig. 1 or such a one as shown in Fig. 2.-'However, it may be desired to utilize a still diflerent mode ofcontrol for these magnets, and an example of a still further controlarrangement is illustrated in Fig. 3. The two coils II are connected inseriesacross the two terminals of the secondary 69. In this seriesconnection are placed one or more condensers 15, the total value ofwhich is much smaller than that needed for resonance. As a result, thecurrent through the coil H and .consequently the variation in themagnetic fields of each of the magnets I3 leads the voltage appliedbetween each of the cathodes 52 and the anode 62. In series with thecoil 14 and the condensers I5 is placed an adjustable resistance 16. Byadjusting the'resistance 16, the angle between the current through thecoils I4 and the voltage applied between the cathodes and the anode ischanged. By referring to Flg.-6, we can see how this relationshipbetween the magnetic field and the applied voltage controls the currentthrough the tube. In Fig. 6, curve 8 represents the variation in voltageapplied between one of the oathodes 52 and the anode 62, and as statedfor Figs. 4 and 5 may also represent at each point the value of currentwhich would fiow through the load device ii if the tube were conductingat that point. Curve t represents the current fiowing through the coilI4, leading the curve s by a certain angle which may be called 0. Curvet thus also represents the variation in the magnetic field oi' each ofthe magnets 13. It should be noted atthis point that these magnets 13may be biased as suggested for the magnets in Fig. 2, although it ispossible to secure sufflcient variation in the fields of these magnets13 without any biasing. The various constants of the magnet 13 may be sochosen that whenever the curve t, as shown in Fig. 6, is at aslightpositive value, the magnetic field of the magnet 13 issufllciently large so that a discharge cannot start between thecorresponding cathode and anode. Thus we see that when the currentthrough coil 14 fol- 1 lows the curve t, the magnetic field issufficiently strong during the initial portion of the voltage cycle 8 soas to prevent a discharge from starting. It is not until the curve tpasses the point it that the corresponding discharge path becomesconducting. Consequently the discharge between the corresponding cathodeand anode will only be conducting between the point a and the point 1:at the end of the voltage cycle a. Thus this discharge path conductsonly but a portion of the positive half of the voltage cycle. If,however, 0 is decreased by increasing the resistance r, the point u willmore closely approach the point 1: and the period of a voltagev cycleduring which the corresponding discharge path is conducting will bedecreased. Consequently the resultant amount of current which flowsthrough this discharge path is decreased. Likewise if 0 is increased bydecreasing the value of the resistance 16, the resultant current throughthe corresponding discharge path will be increased. Instead oftheparticular phase-shifting device illustrated, any suitablephase-shifting device may be employed for changing the phase anglebetween the applied voltage s and the current t through the coil I4. Ifdesired, 'a phaseshifting device may be employed which will enable theoperator to shift the phase of t through 180. Thus the current betweenthe cathode and the anode could be made to start at any point in thepositive half of the applied voltage 3. The above analysis applies withequal force to the discharge space between the other anode and thecathode, except that the curves applying to that discharge space are 180displaced from those shown in Fig. 6. Thus, as explained for Fig. 2, thecurrent due to each half of the voltage cycle is directed through theload device II in the same direction, and the magnitude of this currentis controlled by the variation of the magnetic fields of the magnets 13.

I have found in each of the devices which I have described that itis'ordinarily difilcult to control the discharge by means of thetransverse magnetic field if the load device contains a considerableamount of inductance. I have further discovered, however, that thisdifilculty may be entirely eliminated by placing a bypass resistancearound the discharge path so that a small amount of alternating currentmay initially pass through the inductance of the load device. The valueof this shunting resistance may be sumciently high so that the amount ofcurrent so flowing is negligible with respect to the total loadcurrent.In Fig. 3 I have shown such shunting resistances at 11 and 18, each ofsaid resistances being in parallel with the discharge path between oneof the cathodes and the anode. With a tube having dimensions, such as Ihave referred to above, and having 110 volts A. C. impressed betweeneach cathode and the anode, each of the resistances I1 and 18 were about500 ohms. With such an arrangement, an inductive load of considerableamperage was readily controlled. Of course it is to be understood thatwherever I have quoted particular dimensions and figures, such are forthe purpose of illustration only and are not to be construed in anylimiting sense inasmuch as these particular values will be different ineach application of my device and can have a very' wide range of values.Other arrangements for controlling an inductive load could be used, suchas, for example, bypassing oi the load itself with a capacity in orderto reduce the resultant alternating current impedance.

I wish it to be understood that the various control systems, as shown inFigs. 1. 2 and 3, can

be used interchangeably in each of the devices as shown in any of saidfigures. In addition, any other suitable control circuit may beutilized.

For example, the tubular member ll instead of being connected to anode 8merely through a resistance could be left entirely free. With such anarrangement, the electrons forced over to the member ii would charge itnegatively and thus attract positive ions which would neutralize thenegative charge. In this manner the removal of electrons and positiveions from the discharge path can be accomplished, although the effectmay be less than if the resistance 22 were provided. However, theabovearrangement still produces the fieldrec space together with its variousadvantages as well as other factors which result in the fact that thedischarge in such a device can also be easily controlled by thetransverse magnetic field. Also the tubular member I I could be biasedwith respect to the anode 8 by any suitable source of voltage. These andvarious other circuit connections will readily suggest themselves tothose skilled in the art. Any other desired arrangement of electrodescan-also be utilized, it being merely necessary to provide at least twoelectrodes adapted to have an electrical discharge between them to whichdischarge path my novel control may be applied.

The invention is not limited to the particular details of construction,materials, quantities and values, or processes as described above, asmany equivalents will suggest themselves to those skilled in the art. Itis accordingly desired that the appended claims be given a broadinterpretation commensurate with the scope of the invention within theart.

What is claimed is:

1. A space discharge device comprising a hermetically sealed envelopeenclosing two electrodes in an ionizable atmosphere, said electrodesadapted to support a discharge between them, the pressure of saidatmosphere b'eing sufliciently high to produce intense ionization uponthe passage of said discharge, said envelope being provided with atubular section surrounding a portion of the discharge path between saidelectrodes, a hollow tubular electrically-conductive member positionedwithin said tubular section, the transverse cross-section of saidtubular member being substantially equal in size and shape with theinside transverse cross-section of said tubular section, whereby theouter wall of said tubular member lies closely adjacent the inner wallof said tubular section, and means for impressing a magnetic field onthe discharge space within said hollow tubular electrically-conductivemember and transversely to said discharge path within said hollowmember.

2. A space discharge device comprising a hermetically sealed envelopeenclosing a thermionic cathode, two anodes cooperating with said cathodeand adapted to support a discharge with said cathode, an ionizableatmosphere in said envelope at a pressure sufliciently high to produceintense ionization upon the passage of said discharge, a separateelectrically-conductive member having an extended surface within saidenvelope surrounding the discharge path between each anode and saidcathode, and means for impressing a magnetic field on each of thedischarge paths surrounded by said electrically-conductive members andtransversely to said discharge path.

3. A space discharge device comprising a hermetically sealed envelopeenclosing an anode,

two thermionic cathodes cooperating with said anode and adapted tosupport a discharge withintense ionization upon the passage of saiddischarge, a separate electrically conductive mom- I ber having anextended surface within said ensurface within said envelope adjacent thedischarge path between said electrodes, means for impressing betweensaid electrodes an alternating potential, means for impressing on saiddischarge space transversely to said discharge path a magnetic fieldvarying in magnitude at the same frequency asthe voltage applied betweensaid electrodes and out of phase with said applied voltage, and meansfor varying the phase angle between said applied voltage and saidmagnetic field.

5. In combination, a space discharge device comprising a hermeticallysealed envelope enclosing two electrodes'in an ionizable atmosphere,said electrodes adapted to support a discharge between them, thepressure of said atmosphere being sufiiciently high to produce intenseionization upon the passage of said discharge, an electricallyconductive member having an extended surface within said envelopeadjacent the discharge path between said electrodes, means forimpressing between said electrodes an alternating potential, means forimpressing on said discharge space transversely to said discharge path amagnetic field varying in magnitude at.

the same frequency as the voltage applied between said electrodes andopposite to said applied voltage in time phase, means for biasing saidmagnetic field so that'its average value is greater than that which willallow a dischargeto. start between said electrodes, the variations insaid field being such that the minimum values of said field are lessthan that value which will allow a discharge to start between saidelectrodes, and means for controlling the magnitude of said variations.

6. In combination, a space discharge device comprising a sealed envelopeenclosing two electrodes in an ionizable atmosphere, said'electrodes,

tential cycle and to be greater than said value during the other half ofsaid cycle.

'7. In combination, a space discharge device comprising a sealedenvelope enclosing two electrodes in an ionizable atmosphere, saidelectrodes adapted to have impressed thereon an alternating potentialand adapted to support a disl5 trically conductive member having anextended I charge between them, the pressure of said atmosphere beingsuiiiciently high to produce intense ionization upon the passage of saiddischarge, a member surrounding the discharge path between saidelectrodes, means for impressing on the discharge space within saidmember and transversely to said discharge path a varying magnetic field,means for causing the magnetic field to drop below the minimum valuewhich will prevent a discharge from starting between said electrodesduring one-half of the alternating potential cycle and to be greaterthan said value during the other half of said cycle, and means forvarying the time at which the magnetic field passes through said value.

8. A space discharge device comprising an envelope enclosing twoelectrodes in an ionizable atmosphere, said electrodes adapted tosupport a discharge between them, means for controlling the propagationof ionization along the discharge path between said electrodes,comprising means for creating in the discharge path between saidelectrodes an unobstructed substantially field-free space freely exposedto access by the electrons emitted from said cathode during the absenceof said discharge, and means for impressing a magnetic field transverseto the discharge path between said electrodes in said substantiallyfield-free space, the pressure of said atmosphere being sufiicientlyhigh to produce substantial ionization upon the starting of saiddischarge and to cause said discharge to continue in the presence ofsaid. transverse magnetic field.

9. A space discharge device comprising an envelope enclosingtwo'electrodes in an ionizable atmosphere, said electrodes adapted tosupport a discharge between them, means for creating in the dischargepath between said electrodes an unobstructed substantially field-freespace freely exposed to access by the electrons emitted from saidcathode during the absence of said discharge comprising a control unitinterposed between said electrodes, said control unit having aconductive surface positioned adjacent the discharge path between saidelectrodes, and means for impressing a magnetic field transverse to thedischarge path between said electrodes in said substantially field-freespace, the pressure of said atmosphere being sufilciently high toproduce substantial ionization upon the starting of said discharge andto cause said discharge to continue in the presence of said transversemagnetic field.

10. A space discharge device comprising an envelope enclosing twoelectrodes in an ionizable atmosphere, said electrodes adapted tosupport a discharge between them, a control unit interposed between saidelectrodes, said control unit having a conductive surface positionedadjacent the discharge path between said electrodes, said surface beingfreely exposed to access by the electrons emitted from said cathodeduring the absence of said discharge, and means for impressing amagnetic field transverse to the discharge path between said electrodesadjacent said surface, the pressure of said atmosphere beingsufliciently high to produce substantial ionization upon the starting ofsaid discharge and to cause said discharge to continue in the presenceof said transverse magnetic field.

11. A space discharge device comprising an envelope enclosing twoelectrodes in an ionizable atmosphere, said electrodes adapted tosupport a discharge between them, a control unit interposed between saidelectrodes comprising an electrically-conductive member having anextended surface within said envelope surrounding at least in part thedischarge path between said electrodes, said surface being freelyexposed to access by the electrons emitted from said cathode during theabsence of said discharge-and means for impressing a magnetic fieldtransverse to the discharge path between said electrodes adjacent saidsurface, the pressure of said atmosphere being sufiiciently high toproduce substantial ionization upon the starting of said discharge andto cause said discharge to continue in the presence of said transversemagnetic field.

12. A space discharge device comprising an envelope enclosing twoelectrodes in an ionizable atmosphere, said electrodes adapted tosupport a discharge between them, a control unit interposed between saidelectrodes comprising an electrically-conductive member having anextended surface within said envelope surrounding the discharge pathbetween said electrodes, said surface being freely exposed to access bythe electrons emitted from said cathode during the absence of saiddischarge, and means for impressing a magnetic field transverse to thedischarge path within said conductive member, the pres sure of saidatmosphere being sufficiently high to produce substantial ionizationupon the starting of said discharge and to cause said discharge tocontinue in the presence of said transverse magnetic field.

13. A space discharge device comprising an envelope enclosing athermionic cathode and an anode in an ionizable atmosphere, saidelectrodes adapted to support a discharge between them, means forcontrolling the propagation of ionization along the discharge pathbetween said electrodes comprising means for creating in the dischargepath between said electrodes an unobstructed substantially field-freespace freely exposed to access by the electrons emitted from saidcathode during the absence of said discharge, and means for impressing amagnetic field transverse to the discharge path between said electrodesin said substantially field-free space, the pressure of said atmospherebeing sufliciently high to produce substantial ionization upon thestarting of said discharge and to cause said discharge to continue inthe presence of said transverse magnetic'field.

14. A space discharge device comprising an envelope enclosing athermionic cathode and an anode in an ionizable atmosphere, saidelectrodes adapted to support a discharge between them, a control unitinterposed between said electrodes, said control unit having aconductive surface positioned adjacent the discharge path between saidelectrodes, said surface being freely exposed to access by the electronsemitted from said cathode during the absence of said discharge, andmeans for impressing a magnetic field transverse to the discharge pathbetween said electrodes adjacent said surface, the pressure of saidatmosphere being sufficiently high to produce substantial ionizationupon the starting of said discharge and to cause said discharge tocontinue in the presence of said transverse magnetic field.

15. In combination, a space discharge device comprising an envelopeenclosing two electrodes in an ionizable atmosphere, said electrodesadapted to support a discharge between them, the pressure of saidatmosphere being sufiiciently high to produce substantial ionizationupon the charge path between said electrodes adjacent said surface, anelectrical connection between said control unit surface and one of saidelectrodes, and means for limiting the amount of current fiow in saidelectrical connection to a negligible amount as compared with the normalload current fiowing between said cathode and anode.

16. In combination, a space discharge device comprising an envelopeenclosing two electrodes in an ionizable atmosphere, said electrodesadapted to support a discharge between them, the pressure of saidatmosphere being sufiiciently high to produce substantial ionizationupon the passage of said discharge, a control unit interposed betweensaid electrodes, said control unit having a conductive surfacepositioned adja-' cent the discharge path between said electrodes, saidsurface being freely'exposed to access by the electrons emitted fromsaid cathode during the absence of said discharge, and means forimpressing a magnetic field transverse to the discharge path.betweensaid electrodes adjacent said surface, an electrical connection betweensaid control unit surface and one of said electrodes, said connectioncontaining a currentlimiting impedance.

17. In combination, a space discharge device comprising an envelopeenclosing two electrodes in an ionizable atmosphere, said electrodesadapted to support a discharge between them, a control unit interposedbetween said electrodes, said control unit having a conductive surfacepositioned adjacent the discharge path between said electrodes, saidsurface being freely exposed to access by the electrons emitted fromsaid cathode during the absence of said discharge, and means forimpressing a magnetic field transverse to the discharge path betweensaid electrodes adjacent said surface, and means for controlling themagnitude of said magnetic field, the pressure of said atmosphere beingsufiiciently high to produce substantial ionization upon the starting ofsaid discharge and to cause said discharge to continue in the presenceof said transverse magnetic field.

18. In a space discharge device comprising an envelope enclosing twoelectrodes in an ionizable atmosphere, said electrodes adapted tosupport a discharge between them, the pressure of said atmosphere beingsumciently high to produce substantial ionization upon the passage ofsaid discharge, means for controlling the propaga-- tion of ionizationalong the discharge path between said electrodes comprising means forcreating in the discharge path between said electrodes an unobstructedsubstantially field-free space, the method of operating said spacedischarge device which comprises impressing between said electrodes avoltage suflicient to initiate and sustain an ionizing discharge betweensaid electrodes in absence of a transverse magnetic field, impressingupon said substantially field-free space a magnetic field transverse tosaid discharge path therein of suflicient magnitude to prevent saiddischarge from starting, and then lowering the intensity of the magneticfield transverse to said discharge path to such a value that saiddischarge starts under the application of said voltage to saidelectrodes.

19. In combination, an electron discharge device comprising an envelopecontaining a cathode, an anode, and an electron-deflecting chamberpositioned between the cathode and anode, said chamber having adischarge opening, a source of electromotive force connected between thecathode and anode, an ionizable medium in said envelope, means mountedexteriorly of the envelope for causing the electrons in the defiection'chamber to be deflected away from said opening, said means including amagnetic field of sufiicient strength to restrain current from fiowingthrough the opening, and means for varying the strength of the fieldwhereby initiation of the discharge is controlled, said ionizable mediumhaving a pressure under operating conditions sufiicient to support anarc-like dischadrge flowing in the presence of said magnetic fiel 20. Incombination, an, electron discharge device comprising an envelopecontaining a cathode, an anode, and an electron-deflecting chamberpositioned between the cathode and anode, said chamber having adischarge opening in line with the cathode and anode, a source ofelectromotive force connected between the cathode and anode, anionizable medium in said envelope, means mounted exteriorly of theenvelope for causing the electrons in the deflection chamber to bedeflected away from said opening whereby the number of electronsreaching the anode will be less than required to produce sufiicientcumulative ionization to initiate a discharge within the device, saidmeans including a magnetic field of suflicient strength to restraincurrent from flowing through the opening, and means for varying thestrength of the field whereby initiation of the discharge is controlled,said ionizable medium having a pressure under operating conditionssufiicient to support an arc-like discharge fiowing in the presence ofsaid magnetic field.

21. In the art of controlling the initiation of an arc discharge device,said device being energized by alternating current and comprising anenvelope containing a cathode, an anode, a hollow member through whichthe electrons pass on their way to the anode, an ionizable medium insaid envelope at a pressure under operating conditions sufiicient tosupport an arc-like discharge, the method which consists in magneticallydeflecting the electrons emitted by the cathode out of their normalrectilinear paths to such an extent that the number reaching the anodeis less than required to produce sufiicient ionization of the. gaseousmedium to initiate a discharge during a predetermined portion of thepositive half-cycle of the anode voltage and the formation of an arc isrestrained during the said portion of the anode voltage cycle.

22. In combination, an electron discharge device comprising an envelopecontaining a source of electrons, an electron-receiving member and anelectrode mounted therebetween, an ionizable medium in said envelope ata pressure under operating conditions suflicient to support an arclikedischarge, means for producing a magnetic field which intercepts thedirection of said discharge, means including a source of alternatingcurrent for energizing said device and for producing an alternating fluxin said magnetic means, and means including a source of direct likedischarge, means for producing a magenvelope, a plurality of coils onsaid core. a

netlc field which intercepts the direction of said discharge, said meanscomprising a metal core having a pole piece mounted transversely of saidsource of alternating current for energizing said device and one of saidcoils, and a direct current source for energizing the other of saidcoils.

24. In the art of controlling the initiation of a gaseous discharge in adevice containing a cathode. an anode and an ionizable medium by meansof a direct magnetic field, the method which consists in deflectingelectrons emitted by the cathode away from the anode by the directfield, thereby preventing cumulative ionization, and varying the directfield by combining therewith, an alternating field in order to determinewhen the discharge shall start.

25. In the art of controlling the initiation of a gaseous discharge in adevice containing electrodes and an ionizable medium by means of adirect magnetic field, the method which consists in utilizing themagnetic field to cause the electrons to move in such a direction as toprevent inelastic collisions with the positive ions of the lonizable'medium, and varying the field by periodically adding and subtractingvariable amounts of magnetic field whereby elastic ioniz ing collisionsin predetermined amounts between the electrons and positive ions arepermitted and the gaseous discharge starts.

26. In the art of controlling the initiation of a gaseous discharge in adevice containing a cathode, an anode and an ionizable medium by meansof a direct current field, the method which consists in deflectingelectrons emitted by the cathode away from'the anode by the fieldthereby preventing cumulative ionisation, and varyingthedirect-fieldbyperiodically adding and subtracting variable amounts ofmagnetic field whereby cumulative ionisation in apredetermineddegreeispremittedin order tostart-the 2'1. In the art ofcontrolling a gaseous discharge in a device containing a cathode. ananode and an ionizable medium by a direct magnetic field, said devicebeing energized by alternating current and said magnetic field having amaximum strength sui'ilclent to restrain the discharge from flowingduring the positive halfcycles oi anode voltage, the method whichconsists in utilizing the magnetic field to reduce the number ofionizing collisions between the electrons emitted by the cathode and themolecules of the ionizable medium, and varying the-direct field bycombining therewith, a variable alternating magnetic field whereby theposition in each positive half-cycle of anode voltage at which thegaseous discharge starts may be controlled.

28. In combination, a space discharge device comprising an envelopeenclosing two electrodes in an ionizable atmosphere, said electrodesadapted to support a discharge between them, a control unit interposedbetween said electrodes, said control unit having a conductive surfacepositioned adjacent the discharge path between .said electrodes, saidsurface being freely exposed to access by the electrons emitted fromsaid cathode during the absence of said discharge,

means for impressing a magnetic field transverse to the discharge pathbetween said electrodes adjacent said surface, and an electricalconnection between said control unit surface and one of said electrodes,the pressure of said atmosphere being sufilciently high to producesubstantial ionization upon the starting of said discharge and to causesaid discharge to continue in the presence of said transverse magneticfield.

PERCY L. SPENCER.

